The invention relates generally to power converters and more specifically to multilevel configurations of converters.
The utility and importance of power conversion has grown with advantages being achieved in applications such as motor drives, renewable energy systems, and high voltage direct current (HVDC) systems, for example. The multilevel converter is emerging as a promising power conversion technology for various medium and high voltage applications.
Multilevel converters offer several advantages over conventional two-level converters. For example, the power quality and efficiency of the multilevel converter is better than that of two level converters. Also, multilevel converters are ideal for interfacing between a grid and renewable energy sources such as photovoltaic (PV) cells, fuel cells, and wind turbines. Transformer-less multilevel converters have been designed using a modular structure. Such multilevel converters typically include a plurality of power modules that are coupled between DC buses. The modular structure of the converters allows stacking of these converters to provide different power and voltage levels.
Multilevel power converters typically include a plurality of semiconductor switches and energy storage devices that are placed between the input and output terminals. The semiconductor switches and energy storage devices in the converter aid in providing regulated output power at the output terminals. The output power at the output terminals is dependent on the activation of the semiconductor switches and energy present in the energy storage devices.
Control systems and methods have been designed to activate the semiconductor switches such that the output power is maintained at a desired level while voltage observed across the dc bus is maintained at a substantially constant level.
A topology for a multilevel power converter is described in commonly assigned U.S. application Ser. No. 13/629,882, filed 12 Sep. 2012, which is herein incorporated by reference. It would be desirable to have a control system and method to most efficiently and effectively operate such a topology.